The present invention relates to a burner for injecting, such as particulate material, material and relates particularly, but not exclusively, to such a burner for use in an electric arc furnace.
It is well known to provide an electric arc furnace with supplementary oxygen injection lances; operation of such a furnace involves the striking of an arc between electrodes which creates a heating current which passes through the metal to be melted and the injection of supplementary oxygen via the oxygen injection lances, which may be moved closer to or away from the metal as and when desired. Once struck, the arc acts to heat the metal towards its final temperature of about 1620xc2x0 C. to about 1700xc2x0 C. whilst the oxygen acts to oxidize undesirable elements in the metal and causes them to be extracted from the metal and generate an insulating slag layer which floats on the surface of the molten metal. The insulating slag layer acts to protect the electrodes and furnace wall from splattering molten metal. Supplementary oxy/fuel burners are often provided in the furnace wall for assisting the electric arc heating effect. Our European patent application number 0764815 A describes an oxy/fuel burner intended to reduce the problem whereby such burners are unable to penetrate the slag layer adequately during the final and critical heating step in conventional electric arc furnaces.
A further problem with conventional electric arc furnaces occurs when it is necessary to introduce particulate material into the furnace in order to assist in the thermal and/or chemical processes occurring therein. It is difficult to ensure that such particulate material is correctly distributed and/or delivered to the correct region of the furnace.
It is an object of the present invention to reduce and possibly eliminate the above-mentioned problems associated with the introduction of particulate material into furnaces, such as electric arc furnaces.
Accordingly, the present invention provides a burner for use in an electric arc furnace comprising a body portion having a longitudinal axis X and a main outlet located thereon, fuel and primary oxidant outlets upstream of said main outlet and disposed substantially concentrically about axis X, a chamber within the body portion for receiving and mixing said fuel and oxidant and acceleration means downstream of said chamber for causing said mixture of fuel and oxidant to be accelerated towards and out of said main outlet for combustion, wherein means are provided for discharging particulate matter entrained in a secondary oxidant into the flow of accelerated fuel and primary oxidant immediately adjacent and downstream of said accelerating means.
With such an arrangement the oxidant-entrained particulate matter is drawn into the accelerating flow of fuel and primary oxidant to be thoroughly distributed and/or to reach the desired location within the furnace. Where the particulate matter is coal, partial or even total devolatilization can be achieved in the flame, the volatiles providing further fuel for combustion and hence providing fuel savings.
The means for accelerating the flow of fuel and primary oxidant preferably comprises a flow path for the mixture which successively converges and diverges in the direction of flow.
The accelerating means may comprise a Laval nozzle substantially coaxial with axis X, the discharging means being disposed substantially concentrically about axis X. Preferably the discharging means are configured so as to discharge the oxidant-entrained particulate matter substantially parallel to the axis X.
The discharging means may conveniently be in the form of an annulus surrounding the accelerating means, being adapted to discharge the oxidant-entrained particulate matter in a hollow, substantially cylindrical or conical, spray pattern. With such an arrangement, the discharge means may be configured so as to provide a linear flow path for the particulate matter (i.e. a flow path which is substantially parallel along the significant portion of its length) which is particularly suitable when the particulate material is one with significant abrasive qualities, such as iron carbide.
Alternatively, the discharge means may be substantially coaxial with the axis X, the accelerating means being concentrically disposed around the discharge means. The accelerating means may suitably have an outlet in the form of an annular surrounding the discharge means.
In such an arrangement, the acceleration of the fuel and primary oxidant from an annular outlet produces a significant pressure reduction adjacent the discharge means and therefore provides enhanced mixing and penetration of the particulate material. The discharge means may also be shaped and configured so as to accelerate the oxidant-entrained particulate matter discharged therefrom, thereby accelerating the particulate material to an even greater extent.
The present invention also affords a method of operation of a burner for an electric arc furnace, the method comprising accelerating a mixture of fuel and primary oxidant towards and out of a main outlet of a burner body for combustion, and discharging particulate matter entrained in a secondary oxidant adjacent to accelerating flow of fuel and primary oxidant, whereby said oxidant-entrained particulate matter is drawn into the flow of fuel and primary oxidant.
In most electric arc furnace applications the fuel would be natural gas. The primary oxidant may be oxygen or oxygen enriched air and the secondary oxidant for entraining the particulate material is preferably air, although it could be identical to the primary oxidant in some applications. Moreover, although the present invention is described above in relation to the injection of particulate material, we have discovered that certain embodiments of burners in accordance with this invention are particularly suitable for the injection of liquids (such as additional liquid fuel or cryogenic liquids such as liquid oxygen, as may be desirable in certain applications) or for the injection of slurries (i.e. particulate materials entrained in a liquid), as in the drying and/or incineration of waste sludge, such as sewage. In either case, the liquid material is entrained in air, as with the injection of particulate material, but in droplet or atomized form. Accordingly where used herein, and particularly in the claims, the term xe2x80x9cparticulate materialxe2x80x9d should be understood to encompass both discrete droplets of liquid and of particulate material entrained in liquid.